1. Field of the Invention
The present invention relates to a motor, and in particular to a high power motor not utilizing bearings.
2. Description of the Related Art
A conventional motor comprises a shaft, a rotor, and a bearing. The rotor is disposed on the shaft and supported by the bearing, enabling the rotor to rotate smoothly.
Mechanical components reducing friction and bearing loads in rotary and linear drives include ball and roller bearings, sleeve bushings, dynamic bearings, magnetic bearings, and other configurations.
A ball bearing comprises an outer ring, an inner ring, and a plurality of metal balls disposed therebetween. The ball bearing is actuated by rolling of the metal balls. Only one contact point between the metal balls and the inner or outer ring allows easy acceleration of the motor. The structure of the ball bearing, however, is weak and susceptible to impact. In addition, when the motor with the ball bearing is operated, the balls roll at high speeds, resulting in producing high noise level. The structural interface between the balls and the inner and outer rings requires a high degree of accuracy, thus increasing manufacturing costs.
A sleeve bearing is formed by mixing and sintering bronze powder, iron powder, nickel powder, lead powder and other metal powders. Lubricant is applied into the pores of the bearing. The sleeve bearing, when disposed in a motor, is fastened in the central position of the stator. The shaft of the rotor is disposed in the bearing such that a gap is maintained between the bearing and the shaft. When the motor is operated, the lubricant exudes from the bearing such that the rotor rotates in the lubricant. This type of bearing can sustain higher impact than the ball bearing, and manufacturing costs are also reduced. In a motor utilizing the sleeve bearing, however, the lubricant evaporates into gaseous phase as the bearing is operated over long periods. As a result, the shaft directly contacts the bearing such that friction is produced therebetween. Furthermore, nitrides can possibly form at the ends of the bearing, causing damage and increasing noise level. In addition, dust in the air may be drawn into the center of the motor during operation, contaminating the lubricant surrounding the bearing, increasing noise level and occluding moving parts. Furthermore, since the gap between the bearing and the shaft is small, the efficiency in starting the motor is reduced.
A dynamic bearing is a variation of the sleeve bearing. This type of bearing comprises an inner wall with two annular arrays of V-shaped grooves formed therein. During operation, air and lubricant are impelled toward the pointed ends of the grooves forming two oil-gas cushions to support the shaft. In a motor with this type of bearing, the oil-gas cushion, formed at the pointed end of the V-shaped groove, is unable to be dispersed or evaporated. Formation of the groove on the inner side of the dynamic bearing, however, requires precise manufacturing. Furthermore, the gap between the shaft and the bearing must be accurately maintained. Thus, the manufacturing cost is higher than other types of bearings. Moreover, when the motor operates at low speed, the oil-gas cushion is not formed. Thus, the dynamic effect is not achieved at low speeds, such that performance of the dynamic bearing is substantially the same as a sleeve bearing.
A magnetic bearing has a plurality of N-S (north-south) magnetic poles formed on the shaft. The bearing corresponding to the shaft has the same N-S poles formed thereon. During operation, repellant force suspends the shaft in the bearing. Because there is no direct contact between the shaft and the bearing, neither noise nor friction is generated therebetween. The magnetic bearing, however, must be designed with a gap of about 0.2 mm between the shaft and the bearing, such that balanced force toward the center point is generated by each portion of the bearing surrounding the shaft. However, if the position of the shaft is offset by external force or driving force during operation, the imbalance can cause shaft contact with the bearing. This increases noise, shortens lifetime, and can even interrupt normal operation of the motor.
Furthermore, since the magnetic bearing is based on magnetic balance, there are occasions that the motor cannot be smoothly started. Thus, the magnetic bearing is still in an experimental stage, as yet unable to be mass produced.